Multicast and broadcast transmissions currently are treated the same in many wireless networks. To date, similar treatment of these transmission types has not posed any substantial problems since wireless is a broadcast medium by definition and anyone on the same frequency with the appropriate receiver can receive the signal, irrespective of the destination. However, similar treatment of these transmission types is spectrally inefficient and unreliable in a multi-user wireless network.
As an example, an access point (AP) or base station (BTS) has to make sure that a broadcast is sent at a modulation and coding rate that is acceptable to all wireless devices that are currently in communication with it. Therefore, low (more robust and less efficient) transmission rates are commonly selected to accommodate each and every wireless device, even when a majority of the wireless devices support significantly higher (less robust and more efficient) transmission rates.
Another problem with current multicast communication schemes is the lack of feedback from the receiving wireless devices. This makes the multicast transmission inherently unreliable in a changing wireless environment.
Yet another problem in treating multicast transmissions similar to broadcast transmissions is that, if power-save is supported, the AP or BTS has to coordinate the delivery of multicast to all wireless devices. There is no mechanism to allow the formation of secondary multicast groups to support different Delivery Traffic Indicator Maps (DTIMs) in accordance with IEEE 802.11 standards. As a result, wireless devices may wake up more often than needed, which in turn may drain the battery of certain hand-held devices.